The present invention relates to a machine tool for carrying out various workings such as grinding and cutting operations.
Prior art provides various machine tools which are provided with no means for detecting a contact of a tool to a work or workpiece to be worked. In a case where the machine tool is not provided with any contact detection means, it is impossible to know an exact time of contact of the tool to the work. For example, in a case where the tool is fed fast, there is a possibility that the releasing of this fast feeding has been done after the contact even if an operator has done the releasing operation just before the contact in his recognition or assumption and the tool in condition of the fast feeding contacts the work, which may result in a damage of the tool or work, or both. In order to avoid such possibility, in the prior art, it has been obliged to make delay a time of feeding operation for contacting the tool to the work.
Furthermore, in the prior art, there has been also provided a machine tool provided with means for detecting the contact of the tool to the work. For example, in such machine tool provided with the contact detection means, an ultrasonic wave sensor is disposed near the tool, for example, in a grinding solution, or near the work to detect change in vibration of an ultrasonic wave at times before and after the contact of the tool to the work to thereby detect the contacting thereof.
However, in such prior art machine tool, the machine tool itself or a system including the ultrasonic wave sensor is made large in size as well as providing of a complicated structure or arrangement. In particular, when the ultrasonic wave sensor is disposed near a work having an elongated size in its longitudinal direction, a plurality of ultrasonic wave sensors may be required, thus being complicated and inconvenient for the working operation.
The prior art further provides another type of a machine tool provided with means for detecting the contacting, in which an electric power meter is mounted to a driving means for driving the tool to detect change of power consumption before and after the contact of the tool to the work.
In such prior art, however, there is provided a problem of causing delay in detecting time corresponding to a unit time showing a quantity of the electric power energy detected by the electric power meter. The arrangement of an expensive power meter will result in increasing of total constructional cost.
Further, in another aspect, in the prior art machine tool, it is necessary to independently prepare and arrange a measuring device or the like for measuring a shape or size of the work to be worked.
In addition, the measurement of the shape of the work requires to once stop the movement of the workpiece, thus making troublesome the measuring working, being inconvenient.
Furthermore, in the conventional machine tool, when it is required to control a working force, a load cell means is utilized and located between the work and a vibration stopping member for the work, and the working force to be applied to the work is detected from an output from the load cell and adjusted by an operator by adjusting the vibration stopping member in response to the detected value of the working force. Such working also makes troublesome the entire operation of the machine tool, and in a particular case of the workpiece having a spline groove, spiral groove or the like specific shape, the countermeasure for such control has been itself made complicated.
Still furthermore, in the conventional machine tool, recognition or detection of abnormality of a tool and working conditions such as grinding force or resisting force has been done in accordance with a consumed power of an electric power meter provided for a driving means for driving the tool. However, as described hereinbefore, the detected result of the power meter involves a delay by an amount corresponding to a unit time, resulting in difficulty in a precise grasping of the exact working condition.
Still furthermore, in the conventional machine tool, when a minute cutting operation is performed, the resolving power of the cutting is decided by means of servo-motor and encoder. However, in a machine tool utilizing the servo-motor and the encoder, it is required to convert the rotary motion to the linear motion, and this conversion involves a limit in its performance, which makes it difficult to exactly perform the minute cutting working.
Still furthermore, in the conventional machine tool, when dimensions of the work are controlled by a dimension measuring device and it is required to correct working condition in case of a taper or circularity being disordered, such correction has been done by changing a program of a numerical control (NC) means in accordance with a corrected value of the dimension measuring device. This requires the change of the NC program every time the working correction, thus being troublesome and inconvenient.
The conventional machine tools further provide a difficulty for a countermeasure to an occurrence of such as chatter.